The present invention relates to an air shutoff agent (air-barrier agent) used to stably store a reagent component or a substance to be analyzed by preventing an aqueous reagent or an aqueous specimen from being in contact with air. More particularly, the present invention relates to an air-barrier agent which is used to stably store a reagent component or a substance to be analyzed by layering the air-barrier agent over the surface of an aqueous reagent or aqueous specimen, and which does not soil a measuring section of an autoanalyzer during repeated use. The present invention also relates to a method for stably storing an aqueous reagent or an aqueous specimen using the air-barrier agent.
At present, reagents used for clinical examinations are usually supplied as a liquid or in freeze-dried form. Liquid reagents are used as is and freeze-dried reagents are dissolved when used for measurement. Generally, these reagents are allowed to stand unsealed in a cool place during analysis using an autoanalyzer or during preservation.
Reagents in an unsealed state may exhibit insufficient stability. Specifically, measured values or sensitivity may decrease over time depending on the properties of the reagent component. Moreover, coloration of the reagent or an increase in blank values frequently occurs. Therefore, accuracy and precision which are the most important properties for diagnostic reagents may decrease over time. For example, a reagent using an OCPC method is used for determination of calcium in living body fluid. Since monoethanolamine used as a base buffer solution of the reagent absorbs CO2 in air, the pH of the solution is shifted to the acidic side, thereby affecting the measured values.
Depending on the type of specimen, a component to be analyzed may be easily oxidized by oxygen in air. Such a specimen must be prevented from being in contact with air immediately after sampling in order to prevent oxidization from occurring.
As technology for solving the above problems relating to reagents and specimens, the present inventors have proposed a method of stabilizing a reagent or the like by layering an air-barrier agent, which is immiscible with the reagent and has a specific gravity lower than that of the reagent over the reagent or the like (Japanese Patent Application Laid-open No. 185927/1998).
This method can be applied to various reagents and specimens. However, a problem may occur when this method is applied to a reagent used in an autoanalyzer. Specifically, the air-barrier agent layered over the reagent adheres to a reagent suction/regurgitate nozzle of the autoanalyzer. This may cause a slight amount of the air-barrier agent to flow into a reaction vessel together with the reagent when discharging the reagent into the reaction vessel. In the case of a recently used reaction vessel made of a plastic, the air-barrier agent adheres to the wall of the reaction vessel, thereby soiling the surface of the wall by itself and by interaction with other substances.
Therefore, there has been a demand for an air-barrier substance which does not soil a reaction vessel made of any material of an autoanalyzer even if the air-barrier agent flows into the reaction vessel when discharging the reagent over which the air-barrier agent is layered.
The present inventors have conducted extensive studies to solve these problems. As a result, the present inventors have found that an air-barrier agent containing a chain (linear or branched) hydrocarbon and silicone oil does not soil a reaction vessel due to small affinity thereto, and can be widely used for a reaction vessel made of any material. This finding has led to the completion of the present invention.
Specifically, the present invention provides an air-barrier agent for an analytical reagent or specimen comprising a mixture of a chain hydrocarbon and silicone oil which is immiscible with an aqueous reagent or an aqueous specimen and has a specific gravity lower than that of the reagent or specimen.
The present invention also provides a method for stably storing an aqueous analytical reagent or an aqueous specimen comprising layering the above mixture over the surface of the aqueous analytical reagent or aqueous specimen.